The startup, called Essential, is working on a high-end smartphone designed to compete with Apple's iPhone, sources previously told Business Insider.

Business Insider has also heard that Essential was close to completing a large, $100+ million round of funding from major investors that it was expected to announce soon.

Essential's first phone is expected to launch this spring or summer.

The WSJ report says SoftBank's investment would've valued Essential around $1 billion. It's unclear if SoftBank's investment was supposed to be part of the company's new $100 billion Vision Fund, which will invest in tech companies. SoftBank is expected to finish raising for its Vision fund soon. Apple has already committed $1 billion to the fund.

The WSJ report also says that SoftBank planned to use its marketing muscle to promote Essential's new phone, which would've been key for a new player entering the crowded high-end smartphone market dominated by Samsung and Apple.

A spokesperson for Essential declined to comment. A spokesperson for SoftBank did not respond to requests for comment.